1. Field of the Invention
The present invention relates to an intake device for a motorcycle, particularly of straddle-type, in which an engine and an air cleaner disposed behind the engine are connected to each other through an intake air passage, a rear cushion unit is disposed between the engine and the air cleaner, and an intake temperature sensor for sensing intake air temperature is specifically provided.
2. Related Art
In a general straddle type motorcycle, for example, as disclosed in Japanese Patent Application Laid-open Publication Nos. 5-085454 and 2006-193026 (Patent Publications 1 and 2), a layout in which an engine is disposed in a front half of a vehicle body frame, a fuel tank is disposed above the engine, and a rider's seat is disposed behind the fuel tank, an air cleaner is disposed below the rider's seat, a rear cushion unit which suspends a rear wheel in a cushioning manner is disposed between the engine and the air cleaner at substantially vertical posture is employed.
The engine is disposed in such a posture that a cylinder assembly stands substantially vertical or forwardly inclining attitude on an upper surface of a crankcase, and an intake port opened at a back surface of the cylinder assembly and the air cleaner are connected to each other through an intake air passage. It is preferable to make the intake air passage is as short and straight as possible to reduce the intake air resistance of the engine and to make greater the passage cross sectional area.
However, since the rear cushion unit is disposed between the engine and the air cleaner, the intake air passage can not easily be formed straightly because the rear cushion unit becomes an obstruction. Therefore, the intake air passage has to be formed straight by disposing the intake air passage above the upper mounting portion of the rear cushion unit as in the motorcycles of the Patent Publications 1 and 2.
To achieve the above structure, it is necessary to lower the position of the upper end of the rear cushion unit or to raise the position of the air cleaner. According to the former idea, the entire length of the rear cushion unit should be shortened and the suspension stroke of the rear wheel should be reduced, thus being disadvantageous.
On the other hand, according to the latter idea, the rider's seat should be brought up and the riding comfort will be deteriorated. If the position of the lower end is lowered to increase the entire length of the rear cushion unit, the minimum road clearance is lowered and the off-road running performance is deteriorated, thus being inconvenient.
Furthermore, in recent years, many engines have fuel injection devices as means for supplying air-fuel mixture to the engines. It is necessary for the fuel injection device to sense throttle opening, engine speed, engine temperature, outside air temperature, atmospheric pressure, intake air temperature and the like using a sensor, to process such information by a computer, to obtain a correction value and to inject the most appropriate and necessary amount of fuel directly to an intake air passage of the engine by a fuel injector.
The fuel injection device has merits that the combustion efficiency is excellent, output can be enhanced, and since only a necessary and minimum amount of fuel is injected, fuel consumption amount is small.
Among the sensors, the intake air temperature sensor which senses the intake air temperature detects a temperature of air passing through the intake air passage and introduced into a combustion chamber of the engine. The intake air temperature sensor is subjected to various restraints when the intake air temperature sensor is disposed in each member constituting the intake air passage.
Generally, the intake air temperature sensor is mounted on an air cleaner box body as disclosed, for example, in Japanese Patent Application Laid-open Publication No. 4-94434 (Patent Publication 3), or mounted inside the air cleaner box as disclosed, for example, Japanese Patent Application Laid-open Publication No. 2006-188952 (Patent Publication 4).
When the intake air temperature sensor is mounted on the air cleaner box body, since the intake air does not flow uniformly in the box and the air cleaner box body has a box-like shape, a temperature of only a small portion of air can be detected, which is not preferable in terms of precision.
When the intake air temperature sensor is mounted inside the air clear box, there is an adverse possibility that a temperature of remaining air in the box is detected, which is also not preferable in terms of precision.
In the case of an off-road motorcycle, an exhaust system is disposed near the air cleaner box body in some cases. If the intake air temperature sensor is mounted on the air cleaner box body, heat generated by the exhaust system exerts an adverse influence on the intake air temperature sensor.